In general, a monolithic ceramic capacitor, which is a main use of the dielectric ceramic according to an aspect of the present invention, is manufactured in a manner as described below.
Ceramic green sheets containing a dielectric ceramic material are prepared. For example, the dielectric ceramic material to be used contains BaTiO3 or (Ba,Ca)TiO3 as a primary component. An internal electrode is formed on the surface of this ceramic green sheet by applying an electroconductive material with a predetermined pattern.
A plurality of ceramic green sheets including the ceramic green sheets provided with the internal electrodes are laminated and bonded by thermal compression, so that an integrated green ceramic laminate is prepared.
The resulting green ceramic laminate is fired and, thereby, a sintered ceramic laminate is produced. The internal electrodes composed of the above-described electroconductive material are disposed in the inside of this ceramic laminate.
External electrodes are formed on outer surfaces of the ceramic laminate in such a way as to be electrically connected to specific internal electrodes. For example, the external electrodes are formed by applying an electroconductive paste containing an electroconductive metal powder and glass frit on the outer surfaces of the ceramic laminate, followed by baking. In this manner, a monolithic ceramic capacitor is completed.
In recent years, the demand for miniaturization of the monolithic ceramic capacitor has become even more intensified, and the dielectric material to be used therein has been required to have a high dielectric constant. At the same time, the dielectric material must also satisfy a good dielectric constant temperature characteristic and good reliability in a thin layer monolithic ceramic capacitor. Such a dielectric material is disclosed in Patent Document 1.
The dielectric ceramic in Patent Document 1 has a composition containing a primary component represented by a general formula ABO3 and an additional component including a rare-earth element, and has a ceramic structure composed of crystal grains containing the ABO3 as a primary component and grain boundaries between the crystal grains, wherein the distribution of rare-earth element concentration satisfies the condition that the rare-earth element concentration in the grains/the rare-earth element in grain boundaries is ½ or less and satisfies the condition that 20% to 70% of crystal grains have a rare-earth element distribution in which the concentration in the center is at least 1/50th of that in the area extending from the surface inward to about 5% of the diameter.
Consequently, it is possible to realize a high dielectric constant, small changes in dielectric constant with temperature and small changes in dielectric constant with time under application of a direct current voltage, a high product (CR product) of insulation resistance and electrostatic capacity, and a long accelerated life of insulation resistance under a high temperature and a high voltage.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2002-274936 (corresponding to U.S. Pat. No. 6, 556,423)